A semiconductor device is manufactured by repeating a process of transferring patterns formed with photomasks on the surface of a wafer by means of lithography or etching. In this manufacturing process, in order to realize early boosting of yield and stable operation of the manufacturing process, it is essential to rapidly analyze a defect found by an inline wafer inspection and use the result for countermeasures. The key to rapid application of the analysis result to countermeasures for defects is an automated defect review and classification technology whereby a large number of defects are rapidly reviewed and classified according to the causes. As the manufacturing process becomes microminiatuarized, defect sizes affecting the yield of semiconductor are becoming micromiatuarized, and consequently it is becoming difficult for an optical review apparatus to perform a review with high resolution. To address this problem, SEM (Scanning Electron Microscope) based review apparatuses capable of reviewing at high speeds and with high resolution have been commercialized. In such apparatuses, it is important for detection of microscopic foreign particles or scratches to obtain a shadow image from an SEM image, which is equivalent to a shadow made when those objects are irradiated from the side.
The basic principle of obtaining such a shadow will be described with reference to FIGS. 2A to 2C. A bump 101 created by a foreign particle in the film is scanned as shown by 41 with an electron beam 37, and when the electron beam 37 is scanning the right side of the bump 101 secondary electrons 38 are emitted. At this time, noting a low angle component of the elevation angle, some of the secondary electrons emitted at the left side are hidden by the bump 101. Because of this, the number of secondary electrons detected is different between right and left detector plates 11 and 12. Thus, the images detected by the detector plate 11 and 12 will be ones whose shadows are emphasized as shown in FIGS. 2B and 2C, respectively.
An example is described in JP-A No. 273569/1997 that is intended to achieve high resolution needed for detecting microscopic asperity based on this principle. An electromagnetic overlapping objective lens is used to achieve high resolution. In this case, secondary electrons emitted from the specimen rotate and cause energy distribution, and their rotation angles differ depending on the energy. As a result, even a secondary electron emitted at a certain azimuth will lose its directional information after it has passed through the objective lens. Therefore, the directional information is preserved by generating an electric field near the wafer to accelerate secondary electrons, and causing the secondary electrons to pass through a magnetic field generated by the objective lens at high speeds, whereby to reduce the energy distribution. Furthermore, by controlling the trajectories of secondary electrons and back scattering electrons, secondary electrons are detected by a ring-shaped detector plate disposed between electron source and objective lens; specifically back scattering electrons are detected by the inner ring and secondary electrons by the outer ring. The outer ring is divided into four parts in a fan-like form and the azimuths of secondary electrons can be selected, making it possible to obtain shadow images.
An example of selecting the elevation angle components is described in JP-A No. 30654/2000. In this example, two detector plates are disposed at locations shifted from each other in the direction of light axis, with the distance between the detector plates being at least 25% of the distance between the specimen side detector plate and the focal plane of the objective lens. This allows the selection of detected electrons based on the emission angles of emitted electrons.